The following paragraphs are not an admission that anything discussed in them is prior art or part of the knowledge of persons skilled in the art.
It is common practice to segregate petroleum substances of high viscosity and density into two categories, “heavy crude oil” and “bitumen”. For example, some sources define “heavy crude oil” as a petroleum that has a mass density of greater than about 900 kg/m3 and an American Petroleum Institute (API) gravity less than 22°. Bitumen is sometimes described as that portion of petroleum that exists in the semi-solid or solid phase in natural deposits, with a mass density greater than about 1,000 kg/m3 and a viscosity greater than 10,000 centipoise (cP or 10 Pa·s) measured at original temperature in the deposit and atmospheric pressure, on a gas-free basis, and an API gravity less than 10°. Although there is no direct relationship between density and viscosity, an increase in density (i.e. a reduction in API gravity) is generally accompanied by an increase in viscosity. Although these terms are in common use, references to heavy crude oil and bitumen represent categories of convenience, and there is a continuum of properties between heavy crude oil and bitumen. Accordingly, references to heavy crude oil and/or bitumen herein include the continuum of such substances, and do not imply the existence of some fixed and universally recognized boundary between the two substances. In particular, the term “heavy crude oil” includes within its scope all “bitumen” including hydrocarbons that are present in semi-solid or solid form.
Heavy crude oil may be produced from oil sands, for example by recovery using a thermal in-situ recovery process, such as: steam-assisted gravity drainage (SAGD), expanding solvent steam-assisted gravity drainage (ES-SAGD), cyclic steam stimulation (CSS), steamflooding, solvent-assisted cyclic steam stimulation, toe-to-heel air injection (THAI), or a solvent aided process (SAP).
The greater viscosity and density of heavy crude oil, in comparison to light crude oil, presents challenges associated with transportation. A diluent may be added to the heavy crude oil to facilitate its flow through a pipeline, or to facilitate its handling before, during, or after rail transportation. The diluent is a liquid petroleum that is less viscous than the heavy crude oil, and sufficient diluent is added to reduce the viscosity of the diluent-heavy crude oil blend to a level that allows for the diluent-heavy crude oil blend to be transported.
Diluent may be used to enhance oil and water phase separation of a heavy crude oil/water emulsion produced during an oil sands recovery process. During production of the heavy crude oil, diluent that is added to a heavy crude oil/water emulsion may be vaporized and a portion of the vaporized diluent may be subsequently combusted as fuel gas. Combustion of the vaporized diluent represents a cost for heavy oil production.